Thursday, March 19, 2020

What You Need To Know About Cinco de Mayo in English and Spanish

What You Need To Know About Cinco de Mayo in English and Spanish  ¿Quà © es el Cinco de Mayo? What is Cinco de Mayo? This bilingual feature has been written with classroom use in mind - a grammar guide at the end provides useful tips for Spanish students. En espaol: Los orgenes del Cinco de Mayo Muchos creen que el cinco de mayo es el aniversario de la independencia mexicana. Pero no tienen razà ³n - el dà ­a de independencia en Mà ©xico es el 16 de septiembre. Para familiarizarse con los orà ­genes de la celebracià ³n, es necesario estudiar los sucesos a mediados del siglo diecinueve. Despuà ©s de la Guerra Mexicana Americana, Mà ©xico enfrentaba una crisis econà ³mica. En 1861, Benito Jurez, el presidente mexicano, declarà ³ que Mà ©xico aplazarà ­a por dos aà ±os los pagos de deudas exteriores. Aunque Jurez hubo dicho que se reanudarà ­an los pagos en 1863, la promesa no satisfizo a Gran Bretaà ±a, Francia y Espaà ±a. Se ablandaban Gran Bretaà ±a y Espaà ±a, pero Francia insistià ³ en obtener su dinero por la fuerza. Napoleà ³n III, emperador de los franceses, nombrà ³ un pariente, archiduque Maximillian de Austria, el là ­der de Mà ©xico. Mientras marchaba hacia la Ciudad de Mà ©xico, el ejà ©rcito francà ©s enfrentaba resistencia tenaz. El 5 de mayo, 1862, el general Ignacio Zaragoza y su ejà ©rcito mexicano vencieron el ejà ©rcito francà ©s en la batalla de Puebla. La victoria mexicana era una sorpresa porque el ejà ©rcito francà ©s era ms grande y tenà ­a materiales superiores. Segà ºn  un refrn inglà ©s, es posible ganar la batalla y perder la guerra. Los franceses ganaron otras batallas, y Maximillian se hizo là ­der en 1864. Pero los franceses, enfrentando resistencia mexicana y presià ³n de los Estados Unidos, retiraron las tropas en 1867. El Cinco de Mayo es un dà ­a para conmemorar el coraje de los luchadores contra la opresià ³n. Quizs por eso este dà ­a de fiesta es muy popular dondequiera haya personas de ascendencia mexicana. Por ejemplo, la fiesta hoy dà ­a es muy popular en Estados Unidos, donde viven muchas persons con antepasados de Mà ©xico. In English: Origins of Mexicos Cinco de Mayo Many people believe that May 5 is the anniversary of the Mexican Independence. But theyre mistaken, for the Mexican Independence Day is September 16. To understand the origins of the celebration, you need to go back to the middle of the 19th century. After the Mexican-American War of 1846-48, Mexico was in a fiscal crisis. In 1861 Mexican President Benito Jurez declared that Mexico was suspending payment on all its foreign debt for two years. Even though Jurez had said payments would resume in 1863, Great Britain, France and Spain were not satisfied. Although the British and Spanish-backed off, France insisted on using force to secure its debt payments. French Emperor Napoleon III named a relative of his, Archduke Maximillian of Austria, as ruler of Mexico. As it was marching toward Mexico City, the French Army encountered stiff resistance. On May 5, 1862, General Ignacio Zaragoza defeated the French Army in the Battle of Puebla. The Mexican victory was a surprise, for the French Army was larger and better equipped. There is a saying that its possible to win the battle and lose the war. The French won other battles, and Maximillian became the ruler in 1864. But facing Mexican resistance and American pressure, the French withdrew their troops in 1867. Cinco de Mayo is a time to recognize the bravery of those who fight against oppression. Perhaps that is why this holiday is popular wherever there are people of Mexican descent. For example, the fiesta these days is very popular in the United States, where many people who have Mexican ancestors live. Grammatical Highlights Differences in uses of the two simple past tenses of Spanish can be seen in the article. In general, the preterite is used here in referring to ordinary events (such as with ganaron for the winning of battles), the imperfect is used to provide background, such as in the use of tenà ­an  materiales (literally had materiel). Names of the months typically arent capitalized in Spanish. The name of the holiday is, however. Adjectives such as mexicana and francà ©s derived from names of countries also arent capitalized, nor are most titles such as archiduque. Note how reflexive verbs such as familiarizarse and reanudarse (in the form se reanudarà ­an) are used. Alhough the two verbs could be translated literally in this context as to famliiarize oneself and to resume themselves, such a translation would be awkward. In the third paragraph, a comma is used after France in English but not after Francia in Spanish. That is because Spanish does not use the Oxford comma before the y (and) in a series of words.

Tuesday, March 3, 2020

Calcite and Aragonite in Earths Carbon Cycle

Calcite and Aragonite in Earth's Carbon Cycle You may think of carbon as an element that on Earth is found mainly in living things (that is, in organic matter) or in the atmosphere as carbon dioxide. Both of those geochemical reservoirs are important, of course, but the vast majority of carbon is locked up in carbonate minerals. These are led by calcium carbonate, which takes two mineral forms named calcite and aragonite. Calcium Carbonate Minerals in Rocks Aragonite and calcite have the same chemical formula, CaCO3, but their atoms are stacked in different configurations. That is, they are polymorphs. (Another example is the trio of kyanite, andalusite, and sillimanite.) Aragonite has an orthorhombic structure and calcite a trigonal structure. Our gallery of carbonate minerals covers the basics of both minerals from the rockhounds viewpoint: how to identify them, where theyre found, some of their peculiarities. Calcite is more stable in general than aragonite, although as temperatures and pressures change one of the two minerals may convert to the other. At surface conditions, aragonite spontaneously turns into calcite over geologic time, but at higher pressures aragonite, the denser of the two, is the preferred structure. High temperatures work in calcites favor. At surface pressure, aragonite cant endure temperatures above around 400Â °C for long. High-pressure, low-temperature rocks of the blueschist metamorphic facies often contain veins of aragonite instead of calcite. The process of turning back to calcite is slow enough that aragonite can persist in a metastable state, similar to diamond. Sometimes a crystal of one mineral converts to the other mineral while preserving its original shape as a pseudomorph: it may look like a typical calcite knob or aragonite needle, but the petrographic microscope shows its true nature. Many geologists, for most purposes, dont need to know the correct polymorph and just talk about carbonate. Most of the time, the carbonate in rocks is calcite. Calcium Carbonate Minerals in Water Calcium carbonate chemistry is more complicated when it comes to understanding which polymorph will crystallize out of solution. This process is common in nature, because neither mineral is highly soluble, and the presence of dissolved carbon dioxide (CO2) in water pushes them toward precipitating. In water, CO2 exists in balance with the bicarbonate ion, HCO3, and carbonic acid, H2CO3, all of which are highly soluble. Changing the level of CO2 affects the levels of these other compounds, but the CaCO3 in the middle of this chemical chain pretty much has no choice but to precipitate as a mineral that cant dissolve quickly and return to the water. This one-way process is a major driver of the geological carbon cycle. Which arrangement the calcium ions (Ca2) and carbonate ions (CO32–) will choose as they join into CaCO3 depends on conditions in the water. In clean fresh water (and in the laboratory), calcite predominates, especially in cool water. Cavestone formations are generally calcite. Mineral cements in many limestones and other sedimentary rocks are generally calcite. The ocean is the most important habitat in the geological record, and calcium carbonate mineralization is an important part of oceanic life and marine geochemistry. Calcium carbonate comes directly out of solution to form mineral layers on the tiny round particles called ooids and to form the cement of seafloor mud. Which mineral crystallizes, calcite or aragonite, depends on the water chemistry. Seawater is full of ions that compete with calcium and carbonate. Magnesium (Mg2) clings to the calcite structure, slowing down the growth of calcite and forcing itself into calcites molecular structure, but it doesnt interfere with aragonite. Sulfate ion (SO4–) also suppresses calcite growth. Warmer water and a larger supply of dissolved carbonate favor aragonite by encouraging it to grow faster than calcite can. Calcite and Aragonite Seas These things matter to the living things that build their shells and structures out of calcium carbonate. Shellfish, including bivalves and brachiopods, are familiar examples. Their shells are not pure mineral, but intricate mixtures of microscopic carbonate crystals bound together with proteins. The one-celled animals and plants classified as plankton make their shells, or tests, the same way. Another important factor appears to be that algae benefit from making carbonate by ensuring themselves a ready supply of CO2 to help with photosynthesis. All of these creatures use enzymes to construct the mineral they prefer. Aragonite makes needlelike crystals whereas calcite makes blocky ones, but many species can make use of either. Many mollusk shells use aragonite on the inside and calcite on the outside. Whatever they do uses energy, and when ocean conditions favor one carbonate or the other, the shell-building process takes extra energy to work against the dictates of pure chemistry. This means that changing the chemistry of a lake or the ocean penalizes some species and advantages others. Over geologic time the ocean has shifted between aragonite seas and calcite seas. Today were in an aragonite sea that is high in magnesium- it favors the precipitation of aragonite plus calcite thats high in magnesium. A calcite sea, lower in magnesium, favors low-magnesium calcite. The secret is fresh seafloor basalt, whose minerals react with magnesium in seawater and pull it out of circulation. When plate tectonic activity is vigorous, we get calcite seas. When its slower and spreading zones are shorter, we get aragonite seas. Theres more to it than that, of course. The important thing is that the two different regimes exist, and the boundary between them is roughly when magnesium is twice as abundant as calcium in seawater. The Earth has had an aragonite sea since roughly 40 million years ago (40 Ma). The most recent previous aragonite sea period was between late Mississippian and early Jurassic time (about 330 to 180 Ma), and next going back in time was the latest Precambrian, before 550 Ma. In between these periods, Earth had calcite seas. More aragonite and calcite periods are being mapped out farther back in time. Its thought that over geologic time, these large-scale patterns have made a difference in the mix of organisms that built reefs in the sea. The things we learn about carbonate mineralization and its response to ocean chemistry are also important to know as we try to figure out how the sea will respond to human-caused changes in the atmosphere and climate.